In well-known electromagnetic positioning devices, the force of a spring is applied to the armature of an electromagnet. The latter has an iron core with an exciter winding positioned relative to the armature so that the magnetic force of the electromagnet opposes the force of the spring.
In the known apparatus, the time (positioning time) required for the armature to travel from the initial to the final position is in the order of milliseconds.
The switching times required for known piezo-electric positioning devices is in the range of 10 to 100 microseconds, but the length of path which can be reliably controlled is only in the order of a small fraction of millimeters.